Refrigerant System With Variable Speed Scroll Compressor and Economizer Circuit

ABSTRACT

A scroll compressor system having a variable speed drive is utilized. By providing the economizer and/or bypass functions along with the variable speed drive, precise capacity adjustment between the discrete steps is achieved to exactly match load demands at a wide spectrum of operating conditions.

BACKGROUND OF THE INVENTION

This invention relates to a variable speed scroll compressor that isoperable in a refrigerant system with an economizer function and othermeans of capacity modulation.

Refrigerant systems are utilized in many applications to condition anenvironment. In particular, air conditioners and heat pumps are employedto cool and/or heat a secondary fluid such as air entering anenvironment. The cooling or heating load of the environment may varywith ambient conditions, occupancy level, other changes in sensible andlatent load demands, and as the temperature and/or humidity set pointsare adjusted by an occupant of the building.

Thus, refrigerant systems can be provided with sophisticated controls,and a number of optional components and features to adjust coolingand/or heating capacity. Known options include the ability to bypassrefrigerant which has been at least partially compressed by a compressorback to a suction line. This function is also known as an unloaderfunction. This additional step of operation is taken to reduce systemcooling capacity.

Other options include a so-called economizer cycle. In an economizercycle, a refrigerant heading to an evaporator is subcooled in aneconomizer heat exchanger. The refrigerant is subcooled by a tappedrefrigerant that is expanded and then passed through the economizer heatexchanger to subcool a main refrigerant. This tapped refrigerant is thenreturned to an intermediate point in the compression cycle. Thus, theeconomizer cycle provides a step in operation to vary system capacity byswitching between economized and other modes or steps of operation.

In the prior art, controls can be programmed to optionally actuate anyone of these various functions. However, the capacity provided by thesefunctions is increased or decreased in steps. It would be desirable toprovide the ability to vary the capacity while the system is operatingduring any of the above described steps (modes) of operation in acontinuous fashion in order to exactly match external load demands.

Variable speed drives are known for driving compressors at a variablespeed in a refrigerant system. By driving the compressor at a higher orlower speed, the amount of refrigerant that is compressed and circulatedthroughout the system changes, and thus the system capacity can bechanged accordingly.

One increasingly popular type of compressors is a scroll compressor. Ina scroll compressor, a pair of scroll members orbits relative to eachother to compress an entrapped refrigerant. One design configuration ofa scroll compressor utilizes both economizer and unloader functions.Further, this scroll compressor may employ a single port to provide bothfunctions alternatively or simultaneously. This scroll compressor isdisclosed in U.S. Pat. No. 5,996,364. However, this type of scrollcompressor has not been utilized in combination with a variable speeddrive for its motor.

SUMMARY OF THE INVENTION

In a disclosed embodiment of this invention, a scroll compressor isprovided in a refrigerant system with an economizer circuit. The scrollcompressor has a motor that is driven by a variable speed drive. Byselectively utilizing the economizer circuit, and/or the optionalunloader function the controller can increase or decrease the capacityof the refrigerant system. Further, by varying the speed of the motor,capacities in each mode of operation can be additionally adjusted toprovide essentially continuous stepless control.

A controller identifies a desired capacity level, and then achieves thisdesired capacity level by first actuating the economizer cycle ifincreased capacity is desired, or not actuating the economizer cycle ifextra capacity is not required, (or providing additional means ofunloading to reduce the capacity even further) and then determining adesired motor speed for achieving the exact capacity level. Since therefrigerant compressor provides efficient and reliable operation onlywithin a certain speed range, additional steps of capacity reduction,such as the unloader function, with or without the economizer circuitengaged, may be desired and similarly utilized with the correspondingcompressor motor speed adjustment to precisely control the capacitylevel or achieve more efficient unit operation. In one simplifiedmethod, the variable speed is adjusted incrementally within a particularmode of operation (conventional, economized, unloaded, etc.), and thecapacity provided is monitored. When the desired capacity is reached,then the system operates at that new speed. If the capacity still needsto be adjusted, then the speed is adjusted in another incremental step.Similarly, if capacity needs to be reduced, the optional unloaded modeof operation can be engaged either in conjunction with closed or openeconomizer line. Additionally, the controller may monitor the systemefficiency level and select the most desirable mode of operation andmotor speed. In this case, both capacity and efficiency considerationscan be taken into account to establish the optimum unit operation. Onemore mode of unloaded operation can be added to the system operation,where both the economizer circuit and unloader are engagedsimultaneously.

By providing the variable speed drive in combination with the capacityadjustment options mentioned above, the present invention allows an enduser to exactly tailor the system capacity and/or efficiency orcombination of these two parameters to a desired level. The method ofoperation described above would be especially suitable for atransportation refrigeration applications, such as for example containerrefrigeration units, tractor-trailer units or buses, where a wideoperating range of capacity is desired, while at the same time a precisecapacity level control is also needed to maintain the cargo or thecooled environment within a narrow temperature range. As also common inthese refrigeration applications, an additional throttling device, oftencalled suction modulation valve (SMV) is provided to further reduce thecapacity to the level below the level that would be normally achievablethrough unloading mechanisms and reduction in motor speed. Theapplication of the variable speed drive can diminish or even in certaininstances eliminate the need for an additional SMV.

In other features, the scroll compressor is preferably provided with asingle entry port into the compressor for injecting the refrigerant intothe intermediate compression port, and wherein this single port is alsoutilized to route refrigerant to the suction line when the unloaderfunction is actuated.

In a second embodiment, the scroll compressor is a two-stage compressor,with the intermediate port located between the two stages.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a first embodiment refrigerant cycle.

FIG. 1B shows a detail of the scroll compressor of FIG. 1A.

FIG. 2 shows another embodiment refrigerant cycle.

FIG. 3A shows a graph of the capacity provided by the prior art.

FIG. 3B shows a graph of the capacity provided by the prior art.

FIG. 4A shows the capacity provided by the present invention.

FIG. 4B shows the capacity provided by the present invention.

FIG. 5 shows a more precise view of the actual capacity provided by thetypical existing variable speed controls.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A refrigerant system 20 is illustrated in FIG. 1A having a single stagecompressor 22, a controller 42, a variable speed drive 44 and othercomponents as illustrated in this Figure. As is known, a motor 24 forthe compressor 22 can be driven at a variety of speeds such that theamount of refrigerant compressed by the compressor 22 can be varied. Thecompressor 22 is a scroll compressor having an orbiting scroll member 26and a non-orbiting scroll member 28. As is known, a number ofcompression chambers are defined between the two scroll members tocompress an entrapped refrigerant when the orbiting scroll member 26 isdriven to orbit by the electric motor 24. As can be seen, a suction tube30 leads refrigerant into a suction chamber 31 surrounding the motor andleading into the compression chambers. Once the refrigerant iscompressed, it is driven into a discharge chamber 33 communicating witha discharge port 32. The structure of a scroll compressor is known. Asalso shown, an injection line 34, to be disclosed below, communicateswith a port 51 that is positioned at an intermediate compression point.As shown in FIG. 1B, the port 51 may actually be a plurality of portssuch as is disclosed in U.S. Pat. No. 5,996,364.

Refrigerant compressed by the compressor 22 is discharged from thedischarge port 32, and then to an outdoor heat exchanger 46, which wouldbe the condenser in a cooling mode. Fan 47 moves air over the heatexchanger 46. Downstream of the condenser 46 is an economizer heatexchanger 48. As is known, the economizer heat exchanger receives atapped refrigerant line 45 passing through an economizer expansiondevice 49, and a main refrigerant line 41. Although the two flows areshown flowing in the same direction in FIG. 1A, this is merely tosimplify the illustration. In practice, it is generally preferred tohave the two flows flowing in counter-flow arrangement.

The tapped refrigerant in the tap line 45 subcools the refrigerant inthe main line 41, such that after passing through an expansion device52, it will have a higher cooling potential prior to entering anevaporator 54. Fan 55 moves air over the evaporator 54. From theevaporator 54, the refrigerant returns to a suction line 30 leading backto the compressor 22. Variable or constant speed drives 110 are shownassociated with fans 55 and 47, and can be utilized to vary the speed ofthese fans to achieve system control, as known. An optional suctionmodulation valve 61 can be positioned in the suction line 30 between thecompressor 22 and evaporator 54. The tapped refrigerant from the tappedline 45 passes through the return injection line 34 to enter theintermediate compression point or injection port (or plurality of ports)51 in the compressor 22. A bypass line 19 may selectively bypassrefrigerant from the compressor 22 back to the suction line 30 when abypass valve 40 is opened. It should be understood that the economizerexpansion device 49 also preferably incorporates a shutoff feature, or aseparate shutoff device 36 is provided. When the bypass valve 40 isopened, the shutoff device 36 is preferably closed, and when the shutoffdevice 36 is opened, the bypass valve 40 is typically closed; however,it is also possible to operate with both shutoff valve 36 and bypassvalve 40 open. As shown, the same port of the injection line 34 can beused to deliver the refrigerant from the economizer heat exchanger aswell as to bypass the refrigerant back to the suction line. Of course,if so desired the bypass and refrigerant injection functions can utilizedifferent ports, instead of common point 51.

As is known, the bypass valve 40 is opened when less than the fullcapacity of the compressor 22 is desirable. Thus, partially compressedrefrigerant is returned to the suction line 30, and the cooling capacityof the refrigerant system is reduced. If a capacity increase is desired,then the bypass valve 40 is closed. If even further capacityaugmentation is desired, then the bypass valve 40 is closed and theeconomizer expansion device 49 and/or shut-off device 36 are opened toprovide the economizer function. An enhanced capacity is then provided.

The outline 15 is illustrated in FIG. 1A to make clear that therefrigerant system 20 may be incorporated into various items such as arefrigeration container, a refrigerated tractor-trailer unit, a busair-conditioner, etc.

As shown in FIG. 2, a refrigerant system 60 has two stages ofcompression 62 and 64. A variable speed drive 66 can vary the speed ofthe motors for either or both of the compressors 62 or 64. A thirdcompressor stage 161 is illustrated and could also be controlled by avariable speed drive 66, as could a fourth, etc. A downstream dischargeline 68 leads to a condenser 70, and to an economizer heat exchanger 72.A tap line 74 passes through an economizer expansion device 76, and backto a return intermediate pressure line 78. The return line 78 is shownentering at an intermediate point 80 between the two compression stages62 and 64. If the expansion valve 76 is not electronically controlled,then an additional flow device (normally a solenoid valve) needs to beinstalled to selectively engage and disengage the economizer circuit.The bypass line 82 passes through a bypass valve 84 back to a suctionline 86. Downstream of the economizer heat exchanger 72, the mainrefrigerant flow passes through a main expansion device 88, and anevaporator 90 before passing back to the suction line 86. The compressorstages 62 and 64 are both provided by scroll compressors.

An additional, or alternate bypass valve 100 may communicate thedischarge line 68 back to the intermediate line 78. This would allowfurther control of unloaded or bypass operation. Further, while twostages of compression 62 and 64 are possible, it would be within thescope of this invention to provide additional stages.

Again, a suction modulation valve 61 is placed downstream of theevaporator 55 to provide additional throttle into the suction flow inthis embodiment as well.

A control for either refrigerant cycle 20 and 60 is able to identify adesired cooling capacity, and operate the bypass function and/or theeconomizer function as necessary. Thus, as shown in FIG. 3A, the priorart system provides varying stages A, B, C, D of capacity. Stage Acorresponds to operation in economized mode, stage B corresponds tooperation in economized and bypass modes engaged at the same time, stageC corresponds to non-economized mode, and stage D corresponds to bypassmode of operation. If there is an additional SMV, then, as shown in FIG.3B, by throttling the SMV between the modes of operation mentioned abovethe capacity can be adjusted between these modes. However, the SMVoperation is inefficient, and in general should be avoided if possible.

When the systems of FIG. 1A and FIG. 2 include a variable speed drivefor their compressor motors then there can be a stepless capacitycontrol between the base values A, B, C, D, with or without the use ofSMV. Thus, as shown in FIG. 4A, if the system was operating at maximumcapacity at point E1 (which would normally correspond to economizedcircuit engaged and the compressor running at maximum speed) by reducingthe speed of the compressor the capacity can be reduced to point E2. Iffurther reduction is desired the compressor speed is adjusted and theswitch is made to economized mode with bypass engaged. Further, thesystem capacity can be adjusted by varying the compressor speed alongthe line connecting points EB1 and EB2. If further capacity reduction isdesired, the speed can be adjusted once again and the system will moveto the next mode of operation, which would be a non-economized mode.Now, the system capacity can be adjusted by varying the compressor speedalong the line connecting points N1 and N2. If even further reduction incapacity is desired, the speed can be changed once again and the systemwill move to the next operating mode, which would be a bypass mode. Now,the system capacity can be adjusted by varying the compressor speedalong the line connecting points B1 and B2. System operation shown inFIG. 4B is similar to operation in FIG. 4A, except that abrupt changesin speed are avoided by engaging SMV shortly before the change in modeof operation. Also, even though four major modes of operation are shownin FIGS. 3A, 3B, 4A, and 4B, the actual number of modes can be reduced.For example, the system can be operated only in a single economizedmode, and the capacity in this mode can be varied by engaging a variablespeed drive. As another example, it would be possible not to implementan economized/bypass mode of operation. An extension of operationalmodes can be achieved by selectively opening and closing the optionalvalve 100 that can be positioned between the discharge and intermediatecompression lines in FIG. 1A and FIG. 2 arrangements. It should bepointed out that additional modes of operation are possible forcontrolling capacity of the two-stage compressor arrangement where eachor both of these compressor stages can be driven by a variable speeddrive. It also should be noted that what is shown in the FIGS. 4A and 4Bis only an illustration on how the switch between the modes is made, thedecision on when to make the switch, how to adjust the speed and how toengage the SMV would depend on a specific operating condition, loadcharacteristics, efficiency and power considerations. As an additionalimprovement to the system operation, either the condenser fan or theevaporator fan (or both) can be provided with a variable speed drive.

While varying the speed of the compressors provides desirable benefit,there are upper and lower limits imposed on the actual operatingcompressor speed range that would be available to the end user.Typically, a lower limit is defined by reliability requirements tomaintain adequate lubrication of compressor components such as bearingsand compression elements. On the other hand, an upper limit isdetermined by undesirably high power consumption or excessive noise andresultant inefficient operation as well as safety considerations. Theselimits can be utilized at the system design stage to define times whenit would be desirable to switch between modes of operation. The upperand lower speed limits may vary from one application to the other and becondition dependant during the system operation.

FIG. 5 shows how the ramps would typically be achieved. As shown in FIG.5, once a particular mode of operation is selected, the speed can bevaried within that mode and within the speed limits mentioned above.This iterative change is how variable speed drives work in the priorart. If change beyond the speed limits is needed, then the systemswitches to a different mode of operation.

In further aspects, it is known to make the economizer and unloaderfunctions continuously adjustable. Still, providing a variable speeddrive for the compressor will allow even more flexible, reliable andefficient operation to be achieved.

Although preferred embodiments of this invention have been disclosed, aworker of ordinary skill in this art would recognize that certainmodifications would come within the scope of this invention. For thatreason, the following claims should be studied to determine the truescope and content of this invention.

1. A refrigerant system comprising: at least one scroll compressorhaving a variable speed drive for varying a speed of said scrollcompressor, and said scroll compressor being provided with a suctionport, an intermediate pressure port and discharge port; a condenserdownstream of said scroll compressor and an evaporator downstream ofsaid condenser, with an economizer heat exchanger intermediate to saidcondenser and said evaporator, said economizer heat exchangerselectively returning a tapped refrigerant to said scroll compressor; atleast one condenser fan for moving air across said condenser and atleast one evaporator fan for moving air across said evaporator and acontrol for selectively operating said economizer heat exchanger todeliver a tapped refrigerant through said economizer heat exchanger, andback to said compressor, and said control also being operable to varysaid speed of said scroll compressor to achieve levels of capacitybetween a level of capacity with said economizer heat exchanger beingoperational, and a level of capacity without said economizer heatexchanger being operational.
 2. The refrigerant system as set forth inclaim 1, wherein a bypass port is also provided to selectively bypassrefrigerant from said scroll compressor back to a suction line for saidscroll compressor, and said control being operable to vary a speed ofsaid scroll compressor to provide levels of capacity between a level ofcapacity provided when said bypass operation is actuated, and withoutsaid bypass operation being actuated.
 3. The refrigerant system as setforth in claim 2, wherein said bypass port and said intermediatepressure port are provided by the same port.
 4. The refrigerant systemas set forth in claim 2, wherein the delivery of said bypass refrigerantis controlled by a flow control device.
 5. The refrigerant system as setforth in claim 2, wherein said scroll compressor is a single stagecompressor, and said intermediate pressure port within said scrollcompressor also communicates with said bypass port.
 6. The refrigerantsystem as set forth in claim 2, wherein said scroll compressor has atleast two scroll compressor stages, and said intermediate pressure portis between two of said stages.
 7. The refrigerant system as set forth inclaim 2, wherein said control changing said speed of said scrollcompressor in incremental steps.
 8. The refrigerant system as set forthin claim 2, wherein said bypass port selectively communicates anintermediate pressure line receiving said tapped refrigerant back to asuction line leading to said compressor.
 9. The refrigerant system asset forth in claim 2, wherein said bypass is between a discharge linefor compressed refrigerant, and back to the suction line.
 10. Therefrigerant system as set forth in claim 1, wherein said tappedrefrigerant is returned to said intermediate compression port
 11. Therefrigerant system as set forth in claim 1, wherein the delivery of saidtapped refrigerant is controlled by a flow control device.
 12. Therefrigerant system as set forth in claim 1, wherein said system is partof a refrigeration transportation unit.
 13. The refrigerant system asset forth in claim 12, wherein said refrigeration transportation unit isa refrigeration container unit.
 14. The refrigerant system as set forthin claim 12, wherein said refrigeration transportation unit is atractor/trailer unit.
 15. The refrigerant system as set forth in claim1, wherein at least one said evaporator fans having a variable speeddrive for varying a speed of said fan
 16. The refrigerant system as setforth in claim 1, wherein at least one said condenser fans having avariable speed drive for varying a speed of said fan
 17. The refrigerantsystem as set forth in claim 1, wherein there is a suction modulationvalve located downstream of said evaporator.
 18. The refrigerant systemas set forth in claim 1, wherein said scroll compressor is a singlestage compressor.
 19. The refrigerant system as set forth in claim 1,wherein said scroll compressor has at least two stages.
 20. Therefrigerant system as set forth in claim 1, wherein said controlchanging said speed of said scroll compressor in incremental steps. 21.The refrigerant system as set forth in claim 1, wherein said scrollcompressor has at least two scroll compressor stages, and saidintermediate pressure port is between said two stages.
 22. Therefrigerant system as set forth in claim 21, wherein there are more thantwo scroll compressor stages, with said intermediate pressure port beingbetween two of said stages.
 23. The refrigerant system as set forth inclaim 21, wherein a variable speed drive controls both of said twoscroll compressor stages.
 24. The refrigerant system as set forth inclaim 21, wherein at least one of said two scroll compressor stages doesnot have a variable speed drive.
 25. A method of operating a refrigerantsystem having a scroll compressor, and an economizer cycle, along with avariable speed drive for said compressor; determining a desired load onsaid refrigerant system, and determining whether said economizer cycleshould be engaged to meet said desired load; and varying a speed of saidscroll compressor to meet said desired load.
 26. The method as set forthin claim 25, wherein said scroll compressor is further provided with anunloader function, and both said unloader and said economizer providingmodes being used to meet said desired load.
 27. The method as set forthin claim 25, wherein said speed of said scroll compressor is varied inincremental steps.
 28. The method as set forth in claim 25, wherein asuction modulation valve is also provided, and is actuated to vary theoperational function of the refrigerant system to meet said desiredload.